The invention provides high-pressure mercury-vapor discharge lamps having a high output of ultraviolet radiation. When compared with lamps of the type used for general lighting service, the proportion of medium-wave and long-wave ultraviolet radiation, relative to the total radiation output of the lamp, is high for the lamps in the present invention. The said proportion of UV radiation is able to deeply penetrate skin and is therefore useful for therapeutic radiation purposes. The UV radiation is also useful for causing photocatalytic and photochemical reactions.
Because almost all UV effects having a biological utility may be obtained with lamps of the high-pressure mercury-vapor discharge type, such discharge type of lamp is used in most of the conventional lamp structures used as UV radiators.
British patent specification No. 1,290,189 and U.S. Pat. No. 3,590,307 disclose that when using a high-pressure mercury-vapor discharge which also contains iron and/or manganese halide, and optionally tin halide, it is possible to increase the total output of ultraviolet radiation relative to the power input of the radiator and further to increase the relative ratio of long-wave UV-radiation (in the range of wavelengths from 315 to 380 nm (UV-A)) to medium-wave UV-radiation (in the range of wavelengths from 280 to 315 nm (UV-B)). U.S. Pat. No. 3,416,023 discloses a high-pressure mercury-vapor discharge lamp used for irradiation purposes which as a result of the inclusion of cobalt chloride in the fill, emits only long-wave UV and short-wave visible light. Quite generally, the use of, e.g., iron iodide or cobalt iodide or nickel iodide, respectively, in high-pressure mercury-vapor discharge lamps for general lighting service has become known from the article in the "Journal of the Optical Society of America" (1964), Vol. 54, No. 4, pages 532-540, which reports studies directed to the determination of those metal halide additives to the mercury by which highest luminous efficacy and good color rendering of the lamps are obtainable, i.e., the most favorable characteristics of the lamps in the visual spectral range. No reference is had in said paper, however, to the characteristics of the elements iron, nickel, cobalt in the ultraviolet spectral range. U.S. Pat. No. 4,074,164 discloses sunlamps which contain an iron halide in the fill which also contains at least some of mercury, rare earth, and tin halides.
It is an object of the present invention to provide a radiation source of increased integral output in the range of wavelengths from 300 to 400 nm compared with known devices, and particularly wherein the proportion of radiation in the border range between medium-wave and long-wave ultraviolet radiation (310-350 nm) is high.